Chemotaxis of polymorphonuclear leukocytes is one of the critical responses in host defense. Impaired leukotaxis has been demonstrated in increasing numbers of conditions associated with susceptibility of bacterial infections. Leukocyte migration will be measured in vitro, using leukocytes obtained serially from patients with a variety of clinical problems, and from normal healthy volunteers. The mechanisms responsible for alterations in leukotaxis in patients with renal failure will be investigated, with particular evaluation of the effects of hemodialysis therapy. The effects of drug therapy on leukotaxis will be studied using cells and sera from patients receiving medication which might modify leukocyte function. Leukocytes and sera will be collected from volunteers with experimental viral and mycoplasmal respiratory infections. The in vitro conditions are designed to evaluate separately the influence of cellular and humoral factors which might affect leukotaxis. Comparisons will be made between leukocyte migration and other leukocyte functions, such as phagocytosis and killing of bacteria, leukocyte adherence, and histochemical staining for alkaline phosphatase and acid phosphatase will be done. By understanding the factors important in determining leukotaxis, ways may be found to improve this defense mechanism in diseases in which it is impaired.